Adam Mosseri, who was head of product for Instagram and before that the head of Facebook's news feed feature, has been named Instagram's new chief. But that wasn't all the co-founders said. As part of the announcement, the pair responded to concerns that have swept through the tech industry that Facebook CEO Mark Zuckerberg is increasingly "meddling" with the popular app, according to a report from Recode.

In their announcement, they said Mosseri was the most likely to keep a steady hand on the social network, which now counts more than a billion people who log in at least once a month.

"Since we announced our departure, many people have asked us what we hope for the future of Instagram," the pair said in a blog post Monday. "To us, the most important thing is keeping our community -- all of you -- front and center in all that Instagram does. We believe that Adam will hold true to these values and that Instagram will continue to thrive."

For Instagram in particular, these changes come at a time when Facebook is increasingly looking to the photo sharing service, considered a social network in its own right, as an avenue of growth.

After buying Instagram for $1 billion in 2012, Facebook has been able to turn it into one of the most trafficked websites in the world.

It's particularly popular among teens, a recent Pew survey found, ranking it second behind YouTube among the top sites teens say they use. By comparison, roughly half of teens say they use Facebook, lower than that of YouTube, Instagram or Snapchat. That's a far cry from four years ago, when 71 percent of teens reported being Facebook users.

Part of what's helped Instagram's popularity is how successfully it's borrowed ideas from its competitor Snapchat. One of the most popular features now on Instagram and Facebook is called "stories," where people post photos and videos that disappear within a day.